Chimneys are used to vent flue gases and other emissions from fireplaces, furnaces, and low or high combustion chamber burners to the external environment. If there is enough wind, the flue gases and other emissions are blown away and diluted, and air pollution levels do not get too high. However, during still winter nights, there is often a temperature inversion. A temperature inversion traps smoke close to the ground causing higher levels of air pollution.
Many conventional low or high combustion chamber burners, fireplaces, furnaces, and wood burners do not burn fuel efficiently or completely. The unburnt emissions add to the amount of emissions from the chimney flue and contribute to air pollution.
A problem with many existing chimneys is that atmospheric pressure resists the flow of flue gases and emissions from the fireplace through to the upper end of the chimney. The atmospheric pressure typically creates a resistance pressure of about 14 psi within the chimney flue. This resistance can be increased by wind pressure and/or low atmospheric pressure. Wind creates a backpressure within the chimney flue. This backpressure can cause flue gases and emissions to escape from the fireplace into the room, for example when the door of a wood burner is opened.
The resistance can also cause carbon to be deposited inside the chimney flue. The carbon deposits create additional resistance against the flow of flue gases and emissions through the chimney flue. In addition, the carbon absorbs water, for example overnight, which adds to the amount of emissions from the chimney flue.
A variety of chimney covers or cowls are available for use with existing chimneys. In a typical cowl, the flue gases and emissions are forced to change direction within the cowl before they are emitted to the external environment. Changing direction adds to the resistance of the exhaust gases in the chimney flue.
The resistance provided by the downdraft, carbon deposits, and the cowl reduces the efficiency of the fireplace and chimney and increases the amount of unburnt emissions from the chimney flue.
It is an object of at least preferred embodiments of the present invention to provide a cover for a chimney to create a reduced pressure in a chimney flue and thereby reduce emissions from the chimney flue, or to at least provide the public with a useful alternative.